Positive Electrode Active Material for Lithium Secondary Battery, Preparation Method Thereof, and Positive Electrode for Lithium Secondary Battery and Lithium Secondary Battery Which Include the Positive Electrode Active Material

Abstract

A high-nickel positive electrode active material and a method of making the same is disclosed herein. In some embodiments, the material includes a lithium transition metal oxide, wherein the lithium transition metal oxide is secondary particles, wherein each secondary particle is an aggregate of primary particles, and wherein the oxide has an amount of nickel of 80 atm % or more, a first coating layer formed on a surface of the secondary particle and on surfaces of a portion or all of the primary particles, the first coating layer contains nickel and manganese, and has a layered structure, and a second coating layer formed on an outer surface of the first coating layer, the second coating layer contains boron. The active material has improved stability and initial capacity and crack generation at an interface between primary particles is also suppressed.

1 . A positive electrode active material comprising:
 a lithium transition metal oxide, wherein the lithium transition metal oxide is in the form of secondary particles, wherein each secondary particle is an aggregate of a plurality of primary particles, and wherein the lithium transition metal oxide has an amount of nickel of 80 atm % or more, relative to a total amount of metallic elements excluding lithium in the lithium transition metal oxide;   a first coating layer formed on a surface of the secondary particle and on surfaces of a portion or all of the plurality of primary particles, wherein the first coating layer contains nickel and manganese, and has a layered structure; and   a second coating layer formed on an outer surface of the first coating layer, wherein the second coating layer contains boron.   
     
     
         2 . The positive electrode active material of  claim 1 , wherein the lithium transition metal oxide is represented by Formula 1:
   Li a Ni b Co c M 1   d M 2   e O 2   [Formula 1]
   wherein, in Formula 1,   M 1  is at least one selected from manganese (Mn) and aluminum (Al),   M 2  is at least one selected from the group consisting of zirconium (Zr), boron (B), tungsten (W), molybdenum (Mo), chromium (Cr), niobium (Nb), magnesium (Mg), hafnium (Hf), tantalum (Ta), lanthanum (La), titanium (Ti), strontium (Sr), barium (Ba), cerium (Ce), fluorine (F), phosphorus (P), sulfur (S), and yttrium (Y), and   0.9≤a≤1.3, 0.80≤b<1.0, 0<c≤0.2, 0<d≤0.2, and 0≤e≤0.1.   
     
     
         3 . The positive electrode active material of  claim 1 , wherein the primary particles in the plurality has an average particle diameter of 0.1 μm to 0.5 μm. 
     
     
         4 . The positive electrode active material of  claim 1 , wherein the secondary particles have an average particle diameter (D 50 ) of 8 μm to 15 μm. 
     
     
         5 . The positive electrode active material of  claim 1 , wherein the first coating layer has an average thickness of 10 nm to 200 nm. 
     
     
         6 . The positive electrode active material of  claim 1 , wherein the first coating layer is represented by Formula 2:
   Li x [Ni z Mn w ] y O 2   [Formula 2]
   wherein, in Formula 2, 0.8≤x≤1.2, 0.8≤y≤1.2, 0.1≤z≤0.9, and 0.1≤w≤0.9.   
     
     
         7 . The positive electrode active material of  claim 1 , wherein, in the first coating layer, a molar ratio of nickel to manganese is in a range of 1:9 to 9:1. 
     
     
         8 . The positive electrode active material of  claim 1 , wherein, in the first coating layer, a molar ratio of nickel to manganese is in a range of 5:5 to 9:1. 
     
     
         9 . The positive electrode active material of  claim 1 , wherein the first coating layer is included in an amount of 1 part by weight to 5 parts by weight based on 100 parts by weight of the lithium transition metal oxide. 
     
     
         10 . The positive electrode active material of  claim 1 , wherein the second coating layer comprises at least one selected from the group consisting of lithium boron oxide and boron oxide. 
     
     
         11 . The positive electrode active material of  claim 1 , wherein the second coating layer is included in an amount of 0.01 part by weight to 1 part by weight based on 100 parts by weight of the lithium transition metal oxide. 
     
     
         12 . The positive electrode active material of  claim 1 , wherein the positive electrode active material has 1 wt % or less of a lithium by-product remaining based on a total weight of the positive electrode active material. 
     
     
         13 . A method of preparing a positive electrode active material, the method comprising:
 mixing a lithium transition metal oxide with a solution containing a nickel raw material and a manganese raw material, wherein the lithium transition metal oxide is in the form of secondary particles, wherein each second particle is an aggregate of a plurality of primary particles, and wherein the lithium transition metal oxide has an amount of nickel of 80 atm % or more relative to a total amount of metallic elements excluding lithium in the lithium transition metal oxide;   performing a first heat treatment to form a first coating layer on a surface of the secondary particles of the lithium transition metal oxide and surfaces of a portion or all of the plurality of primary particles, wherein the first coating layer contains nickel and manganese, and has a layered structure;   mixing the lithium transition metal oxide having the first coating layer formed thereon with a boron raw material; and   performing a second heat treatment to form a second coating layer on an outer surface of the first coating layer, wherein the second coating layer contains boron.   
     
     
         14 . The method of  claim 13 , further comprising:
 mixing a lithium raw material with a positive electrode active material precursor and sintering the mixture to form the lithium transition metal oxide.   
     
     
         15 . The method of  claim 13 , wherein the lithium transition metal oxide is not subjected to a washing process before mixing with the solution containing the nickel raw material and the manganese raw material. 
     
     
         16 . The method of  claim 13 , wherein the nickel raw material is nickel nitrate, and the manganese raw material is manganese nitrate. 
     
     
         17 . The method of  claim 13 , wherein the first heat treatment is performed at 650° C. to 850° C. 
     
     
         18 . The method of  claim 13 , wherein the boron raw material is boric acid. 
     
     
         19 . The method of  claim 13 , wherein the second heat treatment is performed at 150° C. to 500° C. 
     
     
         20 . A positive electrode comprising the positive electrode active material of  claim 1 . 
     
     
         21 . A lithium secondary battery, comprising:
 the positive electrode of  claim 20 ;   a negative electrode;   a separator disposed between the positive electrode and the negative electrode; and   an electrolyte.